Popular Science | Why does the small sample not match the full sample?

When polyester knitted fabrics are dyed with disperse dyes, why do the small samples not match the large samples? Dyeing factories generally make small samples in the laboratory, and then enlarg...

When polyester knitted fabrics are dyed with disperse dyes, why do the small samples not match the large samples?

Dyeing factories generally make small samples in the laboratory, and then enlarge the samples in the workshop for production. The reasons for the inconsistent color light and color difference between the small samples and the large samples may be as follows.

1. Different gray fabrics

Grey fabrics should be scouring or degreasing before dyeing. The small sample may not undergo pre-processing, or the small sample processing method may be different from the large sample production in the workshop. The moisture content of gray cloth is different, and the different moisture content of the sample has a greater impact. Due to the different moisture content, the weighing is also different. For this reason, it is required that the gray fabric produced as a sample must be completely consistent with the gray fabric produced in the workshop.

In addition, is the gray fabric pre-shaped? If the large sample gray fabric has been pre-shaped, the small sample gray fabric has not been pre-shaped, or even the large sample and the small sample have been pre-shaped, and different setting temperatures can also cause different color absorption.

2. Differences in dyes

Although the dyes used in the small sample and the dye used in the large sample are of the same type and strength, the batch numbers are different or the sample weighing is not accurate enough. This may cause differences between small samples and large samples. It is also possible that the dyes used for large-scale production have agglomerated and become damp, and some dyes are unstable, resulting in a decrease in strength.

3. The ph value of the dye bath is different

General sample master dye bath The ph value is more accurate, but the ph value is unstable or no acid-base buffer is added during the production of large samples. During dyeing, due to the alkalinity of the steam, the ph value rises during the production of large samples. Some disperse dyes, such as those containing ester groups, acyl groups, etc. Amino, cyano, etc. are hydrolyzed under high temperature alkaline conditions. There are also some dyes whose carboxyl groups can be ionized under alkaline conditions, increasing their water solubility and reducing their dye uptake rate. When the pH value of most disperse dyes is 5.5 to 6, the color light is normal and stable, and the dye uptake rate is also high.

But when the pH value increases, the color light changes. For example, dyes such as dispersed black s2bl, dispersed dark blue hgl, dispersed gray m, etc. have obvious color changes when the pH value is >7. Sometimes the gray fabric is not fully washed after pre-treatment and becomes alkaline. During dyeing, the pH value of the dye bath increases, which affects the shade.

4. Bath The influence of ratio

During the small sample test, the liquor ratio is generally larger [1: (25~40)], while the large sample liquor ratio is based on It varies depending on the equipment, generally 1: (8 to 15). Some disperse dyes have little dependence on liquor ratio, and some have great dependence. This causes color difference due to the difference in liquor ratio between the small sample and the large sample.

5. The impact of post-processing

Post-processing is one of the causes of color difference. Especially for medium and dark colors, if reduction cleaning is not performed or the cleaning is not clean, in addition to floating colors, it can also affect the color light and produce a certain color difference. Therefore, the restoration cleaning must be consistent with the small sample and the large sample.

6. The influence of heat setting

Disperse dyes can be divided into high-temperature, medium-temperature and low-temperature types.

The same type of dye should be selected when color matching. In case of high temperature type and low temperature type color matching, the setting temperature should not be too high when heat setting. To prevent the temperature from being too high, causing some dyes to sublimate and affect the color light, resulting in chromatic aberration. The requirements for shaping conditions for small samples and large samples are basically the same.

Because whether the pre-treatment is set or not and the setting conditions (temperature) have a great impact on the color absorption of polyester (the greater the setting degree, the The lower the dyeability), so the cloth used for small samples must be consistent with that of large samples (that is, a semi-finished sample in the workshop is used before production), which is one of the key points.

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